The human knee is a complex joint containing spatially interrelated bones, ligaments, and cartilaginous structures which interact to create a variety of motions. Specifically, the femoral condyles articulate with the surface plateaus of the tibia, through the cartilaginous medial and lateral menisci, and all of these structures are held in place by various ligaments. Undamaged menisci provide shock absorption for the knee by ensuring proper force distribution, stabilization, and lubrication for the interacting bone surfaces within the knee joint, which are routinely exposed to repeated compression loading during normal activity. Much of the shock absorbing function of the medial and lateral menisci is derived from the elastic properties inherent to cartilage.
The meniscus of the knee joint is a half moon shaped piece of cartilage that lies between the weight bearing joint surfaces of the femur and the tibia. It is triangular in cross section and is attached to the lining of the knee joint along its periphery. There are two menisci in a normal knee; the outer one is called the lateral meniscus, the inner one the medial meniscus. The menisci play an important role in absorbing impact loads.
The menisci provide stability to the knee joint. Either of the menisci may tear or split when subjected to certain forces. This injury, which is commonly referred to as torn cartilage in the knee, is painful and may limit mobility.
Undamaged menisci provide shock absorption for the knee by ensuring proper force distribution, stabilization, and lubrication for the interacting bone surfaces within the knee joint, which are routinely exposed to repeated compression loading during normal activity. Much of the shock absorbing function of the medial and lateral menisci is derived from the elastic properties inherent to cartilage. When menisci are damaged through injury, disease, or inflammation, arthritic changes occur in the knee joint, with consequent loss of function.
The meniscus, a cartilaginous tissue, performs several functions in the knee including load transmission from the femur to the tibia, stabilization in the anterior-posterior position during flexion, and joint lubrication. Damage to the meniscus results in reduced knee stability and knee locking. Over 20 years ago, meniscectomies were performed which permitted pain relief, but were subsequently found to induce the early onset of osteoarthritis.
Injury to the knee involving a tear in the meniscus is a common occurrence, often occurring in the context of athletic events, and is prevalent in the younger population. The meniscus is recognized as being vital to the biomechanical stability and protection of the knee joint. Damage to the meniscus can greatly increase the likelihood of the articular surfaces of the knee joint developing conditions such as osteoarthritis. A common remedy which has been previously used for tears in the meniscus involved removal of the meniscus. However, it has been shown that degenerative changes in the knee are directly proportional to the amount of meniscus removed. Thus, in many instances it is desirable to repair the torn meniscus with the objective being to prevent instability of the knee joint and to prevent onset of conditions such as osteoarthritis.
Of the approximately 600,000 meniscal injuries that occur annually in the United States, an estimated 80% of tears are located in the avascular, irreparable zone. Thus instrumentation and a method that repairs “non-repairable” tears by replacement of the damaged meniscus with an allograft implant would be valuable for painless musculoskeletal movement and prevention of the early onset of osteoarthritis in a large segment of the population.
Various repairs and replacements have been used to relieve pain and restore function to the joint where the cartilage has been damaged. For example hyaline cartilage may be damaged by impact injuries or worn down in the course of arthritis. Typically, the ends of the bones forming a joint are cut away and replaced with prosthetic bearings made of metal and plastic to restore pain free articulation of the joint. In cases where the damage occurs as a small localized defect, some investigators have attempted to replace only the small defect by placing a patch of replacement material, natural or synthetic, at the defect.
Current methods for repairing tears in the meniscus are technically very challenging for the surgeon. One widely used technique requires that a long needle with a suture be passed through the torn meniscus and the knee joint. The needle carrying the suture is passed through the meniscus and the knee in its entirety several times until the meniscal tear is closed. As this procedure is typically performed arthroscopically, the amount of space available within the knee for manipulating the long needle through the meniscus is extremely limited. The procedure often requires more than one pair of hands, with one pair inserting the needle into the knee while another pair uses graspers, operating in the limited inflated space in the interior of the knee, to shuttle the needle through the meniscus and out the other side of the knee.
One area of meniscal repair is the use of allograft meniscal tissue used as an implant replacement for the damaged meniscus. U.S. Pat. No. 7,124,762 issued Oct. 24, 2006 discloses a meniscus allograft with an integral bone bridge. The bone bridge is held in a clamp and trimmed with a surgical saw so that it fits into a trapezoidal shaped or dovetail shaped blind end groove cut into the upper surface of the tibia. A rasp is used to create the orthogonal angle of the dovetail transplant.
This type of meniscal allograft transplant is currently being used by Arthrex, Inc. A similar allograft implant having a rectangular bone bridge is trimmed on a cutting board so that the bridge fits into a rectangular groove cut into the tibial surface is used by the Stryker corporation. The rectangular slot on the tibular surface is lined and a hole is drilled parallel to the marker line with the groove being formed by a rasp. The allograft implant and instruments and method of transplantation are shown in U.S. Pat. No. 6,699,252 issued Mar. 2, 2004. A double bone plug meniscus surgical technique is utilized by Cryolife, Inc. with cylindrical bone plugs cut on each end of the horns of the allograft meniscus which are placed in cylindrical blind bores cut into the tibial surface, and held in place by sutures.
Another reference is U.S. Pat. No. 5,092,894 issued Mar. 3, 1992 which discloses a biocompatible meniscus implant constructed of deformable and resilient material with the horns of the meniscus being mounted in tubing which is inserted into cylindrical bores cut into the tibia.
A number of meniscus prostheses have been devised which employ resilient materials such as silicone rubber or natural rubber, as in U.S. Pat. No. 4,344,193 (issued Aug. 17, 1982) and U.S. Pat. No. 4,502,161 (issued Mar. 5, 1985). Meniscal cutting devices have been disclosed in U.S. Pat. No. 4,711,238 (issued Dec. 8, 1987).